1. Field
The present invention relates to a distortion compensator, an optical receiver, distortion compensator and optical receiver controlling methods and an optical transmission system. More specifically, the present invention includes a technique of compensating for waveform distortion generated in an optical transmission line and a device implementing same.
2. Description of the Related Art
In communication networks, optical communication using an optical fiber as an optical transmission line is being frequently used. In order to cope with a recently promoted increase in volume of information flowing through a network, increases in distance and capacity of an optical transmission system used are now being requested. However, waveform distortion exerted on light in an optical fiber is one of factors that restricts the increases in transmission distance and capacity of an optical transmission system. The waveform distortion exerted on light is generally classified into linear distortion and nonlinear distortion. Primary chromatic dispersion and primary polarization mode dispersion are included in the linear distortion. Both the linear distortion and the nonlinear distortion are compensated for in an optical receiver that receives an optical signal from an optical transmission line. The linear distortion may be compensated for by using a digital coherent technique in an optical receiver that receives an optical signal which has been transmitted through an optical fiber. Self phase modulation is included in the nonlinear distortion. Compensation for nonlinear distortion which is realized in an optical receiver is described, for example, in “Optical Express 16, pp 889-896 (2008), by Kazuo Kikuchi”.
According to the technique described in the above mentioned literature, nonlinear distortion generated in an optical fiber is compensated for in an optical receiver. However, as will be described in detail below, the accuracy in compensation is limited.